docs: def Xu_Fang_voidage(x, rhol, rhog, m, D, g=g):
      r'''Calculates void fraction in two-phase flow according to the model 
      developed in the review of [1]_.
      
      .. math::
          \alpha = \left[1 + \left(1 + 2Fr_{lo}^{-0.2}\alpha_h^{3.5}\right)\left(
          \frac{1-x}{x}\right)\left(\frac{\rho_g}{\rho_l}\right)\right]^{-1}
          
      Parameters
      ----------
      x : float
          Quality at the specific tube interval []
      rhol : float
          Density of the liquid [kg/m^3]
      rhog : float
          Density of the gas [kg/m^3]
      m : float
          Mass flow rate of both phases, [kg/s]
      D : float
          Diameter of the channel, [m]
      g : float, optional
          Acceleration due to gravity, [m/s^2]
  
      Returns
      -------
      alpha : float
          Void fraction (area of gas / total area of channel), [-]
  
      Notes
      -----
      Claims an AARD of 5.0%, and suitability for any flow regime,
      mini and micro channels, adiabatic, evaporating, or condensing flow,
      and for Frlo from 0.02 to 145, rhog/rhol from 0.004-0.153, and x from 0 to 
      1.
          
      Examples
      --------
      >>> Xu_Fang_voidage(0.4, 800., 2.5, m=1, D=0.3)
      0.9414660089942093
  
      References
      ----------
      .. [1] Xu, Yu, and Xiande Fang. "Correlations of Void Fraction for Two-
         Phase Refrigerant Flow in Pipes." Applied Thermal Engineering 64, no. 
         1-2 (March 2014): 242–51. doi:10.1016/j.applthermaleng.2013.12.032. 
      '''
      G = m/(pi/4*D**2)
      alpha_h = homogeneous(x, rhol, rhog)
      Frlo = G**2/(g*D*rhol**2)
      return (1 + (1 + 2*Frlo**-0.2*alpha_h**3.5)*((1-x)/x)*(rhog/rhol))**-1